A prior art specimen-holding device for use with an ultra-high resolution transmission electron microscope (TEM) is shown in FIGS. 5 and 6. FIG. 5 is a cross-sectional view taken perpendicular to the optical axis of the electron beam. FIG. 6 is a cross-sectional view taken parallel to the optical axis. It is assumed that the direction of the optical axis of the electron beam lies in the direction of the z-axis. In the plane vertical to the optical axis of the electron beam, the axial direction of the specimen-holding device is taken to lie on the x-axis and the direction perpendicular to the x-axis is taken to lie on the y-axis.
The prior art specimen-holding device, generally indicated by reference numeral 100, has a pipe 113 in which a specimen-holding rod 101 is inserted. Y-motion and z-motion drive units are mounted on the outer surface of the pipe 113. The pipe 113 is totally held to a specimen chamber wall 103 by a spherical bearing 102. The y-motion drive unit incorporates a driving motor (not shown) for shifting a y-motion driving lever 104 (FIG. 5) in the y direction to move the pipe 113 in the y direction against the action of a spring 105. Thus, the specimen-holding rod 101 and a specimen holder 107 inside a specimen chamber 106 are displaced. The holder 107 is connected to the front end of the rod 101. As shown in FIG. 6, the z-motion drive unit has a z-motion driving motor 108 which rotates a z-motion driving lever 110 about a pivot 109. As a result, the pipe 113 is moved in the z direction against the force of a spring 111. These movements in the y and z directions are made via the spherical bearing 102.
Tilt about the x-axis is made by a tilting unit. As shown in FIG. 6, an electric motor (not shown) for tilt about the x-axis rotates a worm gear 114 and a follower gear 115 in mesh with the worm gear 114. This, in turn, rotates the pipe 113. In this way, the specimen-holding rod 101 and the specimen holder 107 can be tilted about the x-axis. Movement in the x direction is made by a driving motor (not shown) via an x-motion driving lever 116 (FIG. 5) which turns about a pivot. In this case, the pressure difference between the vacuum inside the specimen chamber 106 and the outside atmosphere keeps the specimen-holding rod 101 pressed against the lever 116. Under this condition, the x-motion driving lever 116 is moved in the x direction, thus displacing the specimen-holding rod 101 and the specimen holder 107. The inside of the specimen chamber 106 is hermetically isolated from the outside atmosphere by O-rings 118, 119 and 120. Also, the spherical bearing 102 is hermetically isolated from the specimen-holding rod 101 by an O-ring 121.
In electron microscopy, a specimen is required to be placed in position in a short time. At this time, the ranges of movements in the x and y directions are on the order of .+-.1 mm. The range of movements in the z direction is about 0.5 mm. With the above-described prior art specimen-holding device, movements in the x direction are made by the x-motion driving lever 116. In this case, the spherical bearing 102 is hermetically isolated from the specimen-holding rod 101 by the O-ring 121 on which the rod 101 slides. Therefore, the sliding friction created by the O-ring 121 presents problems. Smooth movements in the x direction are not made. Especially, when the rod begins to move, the speed varies greatly. Also, when the rod is brought to a stop, it is not immediately stopped completely. Consequently, it takes some time until the specimen is settled in a desired position.
Moreover, two mechanisms are provided to shift the specimen. In particular, one mechanism makes movement in the y direction, movement in the z direction, and tilt about the x-axis via the spherical bearing 102. The other mechanism makes movement in the x direction via the x-motion driving lever 116. Hence, the specimen-moving mechanism is made complex. Furthermore, considerable space is needed to install the driving mechanisms. This limits positions at which other components, such as an observational unit and an analytical unit, can be installed.